<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    let score = +prompt('输入成绩')
    if (score > 90) {
      alert('成绩优秀')
    } else if (score > 70 && score <= 90) {
      alert('成绩良好')
    } else if (score > 60 && score <= 70) {
      alert('成绩及格')
    } else {
      alert('成绩不及格')
    }
  </script>
</body>

</html>